Zimmermann et at Parasitism by Naobranchia ocadentahs 
373 
Table 1 
Summary of field collection information for northern and southern rock sole from the two sampling areas of the western Gulf of 
Alaska and the central Aleutian Islands. 
Area 
Dates 
Hauls 
Depth range 
(m) 
Temperature range 
(Celcius) 
Gulf of Alaska 
8 to 18 Jun 1996 
18 
46-149 
4. 0-7. 4 
Aleutian Islands 
25 to 27 Jun 1997 
8 
143-232 
3. 9-4. 5 
Table 2 
Summary of fish examined at sea and parasite collections. Mean intensity = average number of parasites for each infested fish. 
Range is from minimum to maximum numbers of parasites for each infested fish. 
Naobranchia occidentalis Nectobrachia indivisa 
Area and 
rock sole species 
Fish examined 
at sea for 
gill parasites 
Fish infested 
with either 
gill parasite 
Prevalence 
(%) 
Mean 
intensity 
Range 
Prevalence 
(%) 
Mean 
intensity 
Range 
Gulf of Alaska 
Northern 
225 
58 
22 
4.4 
1-22 
15 
3.8 
1-21 
Southern 
282 
15 
5 
2.9 
1-13 
1 
2.0 
1-3 
Aleutian Islands 
Northern 
237 
89 
36 
10.2 
1-45 
9 
3.1 
1-8 
analyses. Differences in parasite prevalence between the 
northern and the southern rock sole were determined with 
chi-square tests, and differences in mean intensity were 
determined with Welch’s approximate 1-test (Zar, 1984). 
To test for significant differences in the length-weight 
relationship between parasitized (containing Naobranchia 
occidentci/is or Nectobrachia indivisci , or both) and unpar- 
asitized fish, natural log-transformed length and weight 
data were compared by linear regression. The slopes and 
T-intercepts were compared by using F-ratios. 
Results 
Parasite species 
Four species of copepod parasites were identified from the 
gills of the infested fish. The most common parasite was 
Naobranchia occidentalis Wilson, 1915, which attaches to 
the gill filaments by its modified second maxillae (Kabata, 
1988). This parasite was easily removed in the laboratory; 
freezing and thawing the specimens may, therefore, have 
loosened the parasite’s grip. The next most common para- 
site, Nectobrachia indivisci Fraser, 1920, firmly anchors 
in the filament and could only be removed by cutting 
the filament or breaking off the bulla. Nectobrachia inch- 
visa was almost always found attached to the tips of the 
gill filaments. Two specimens of Acanthochondria vancou- 
verensis were found unattached in the gill chambers of 
two Gulf of Alaska northern rock sole, constituting the 
first record of parasitism in wild rock sole for this species 
(Kabata 1 ). A single specimen of Haemobciphes diceraus 
was found attached on the third gill arch, eyed side, of a 
Gulf of Alaska northern rock sole (Kabata 2 ). Kabata ( 1988) 
reported that all of these parasites occur on rock sole, 
except for A. vancouverensis. Small, highly mobile leeches 
were also frequently noted on the gills of fish caught in 
the Gulf of Alaska survey, but because of their mobility, 
their presence could not be reliably documented. We did 
not attempt to enumerate or identify this species. 
Gulf of Alaska A total of 225 northern and 282 southern 
rock soles were visually examined for parasites at sea 
during the 1996 Gulf of Alaska survey, and 78 rock sole 
heads were collected because they appeared to have at least 
one copepod gill parasite (Table 2). Naobranchia occidenta- 
lis or Nectobrachia indivisa (or both) were found on 73 of 
the collected heads during laboratory dissection (58 north- 
ern and 15 southern rock sole). Only one juvenile female or 
Kabata, Z. 1998. Personal commun. Department of Fisher- 
ies and Oceans, Pacific Biological Station, Nanaimo, British 
Columbia, Canada, V9R 5K6. Kabata suggested that we consider 
this incidence of parasitism by A. vancouverensis to be the first 
record of parasitism in wild rock sole by this species. A former 
record of parasitism by this species was for aquarium fish only. 
Kabata, Z. 1998. Personal Commun. Department of Fish- 
eries and Oceans, Pacific Biological Station, Nanaimo, British 
Columbia, Canada, V9R 5K6. Kabata confirmed our tentative 
identification of Haemobaphes and identified it with fair cer- 
tainty as H diceraus. 
